The exact steps would be solver and solution dependent. The question is to vague to provide a detailed answer.
Recent versions of NX Nastran have dedicated elements for Plane Stress (CPLSTS*) and Plane Strain (CPLSTN*) analysis:
The definition of these is supported in Simcenter Pre/Post. The appropriate 2D Solid option must be set on the FEM to specify the plane that these elements will be defined on